Low mass disc drive suspension

ABSTRACT

A suspension (22, 102, 2190) supports a slider assembly (20, 204) in a disc drive (10). The suspension (22, 102, 190) includes a longitudinal axis (48, 114, 210), a proximal mounting section (40, 106) for mounting to a rigid track accessing arm (24, 204), a distal mounting section (42, 108) for supporting the slider assembly (20, 204), and first and second laterally spaced suspension beams (44, 46, 110, 112, 206, 208) extending from the proximal mounting section (40, 106) to the distal mounting section (42, 108). The first and second suspension beams (44, 46, 110, 112, 206, 208) have inside and outside edges (66, 68, 124, 126) relative to the longitudinal axis (48, 114, 210) and are flat from the inside edges (66, 124) to the outside edges (68, 126). A first preload bend (80, 113, 214) is formed in the first and second suspension beams (44, 46, 110, 112, 206, 208) transverse to the longitudinal axis (48, 114, 210).

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 60/054,164, entitled "LOW MASS SUSPENSION ENABLING MICRO ACTUATION,"filed Jul. 29, 1997.

BACKGROUND OF THE INVENTION

The present invention relates to disc drive data storage systems and,more particularly, to a low mass suspension formed by a pair oflaterally spaced suspension beams.

Disc drive data storage systems use rigid discs which are coated with amagnetizable medium for storage of digital information in a plurality ofcircular, concentric data tracks. The discs are mounted on a spindlemotor which causes the discs to spin and the surfaces of the discs topass under respective hydrodynamic (e.g. air) bearing disc head sliders.The sliders carry transducers which write information to and readinformation from the disc surfaces. Each slider is supported by a trackaccessing arm and a suspension. The track accessing arms move thesliders from track to track across the surfaces of the discs undercontrol of electronic circuitry.

The suspension connects the track accessing arm to the slider. Thesuspension provides a preload force, in the range of 0.5 gmf to 4.0 gmf,which forces the slider toward the disc surface. The preload force isgenerated by forming a preload bend in the suspension, which becomeselastically deformed when the track accessing arm, suspension and sliderare loaded into the disc drive. The preload bend is typically positionednear the proximal end of the suspension, adjacent to the track accessingarm. The suspension has a comparatively rigid portion which transfersthe preload force from the elastically deformed preload bend to theslider. The rigid portion is typically made by forming stiffening websor flanges along the longitudinal edges of the suspension.Alternatively, the rigid portion may be formed by depositing circuitlayers on the suspension material. The rigid portion of the suspensionis typically referred to as a "load beam".

Additionally, the suspension is flexible in the slider pitch and rolldirections to allow the slider to follow the disc topography. This pitchand roll flexibility is obtained from a gimbal structure, which istypically a separate piece part that is welded-to the load beam portionof the suspension. The separate gimbal is usually formed from a thinnermaterial than the load beam to increase its pitch and roll compliance.Alternatively, the gimbal may be formed from partially etched materialor from the load beam material itself. Partially etched gimbals aresubject to wide variations in pitch and roll stiffness as the etchedthickness varies -over a typical range. Gimbals formed from the loadbeam material restrict the suspension to be made of thin stock which cansupport only small preload forces.

The slider includes an air bearing surface which faces the disc surface.As the disc rotates, the air bearing surface pitches and rolls to anequilibrium position wherein a center of bearing pressure is defined onthe air bearing surface. The desired location of the pressure center isdefined as the air bearing load point. Variations in pitch and rollmoments applied by the gimbal cause deviations in the location of thepressure center away from the desired air bearing load point.

The point at which the suspension applies the preload force to theslider is usually directly above the air bearing load point. The preloadforce is typically applied to the slider through a dimple or load buttonwhich bears on the back surface of the slider. Alternatively, thepreload force is applied through the gimbal structure. This point ofpreload application is defined as the suspension load point.

Microactuators are now being developed for adjusting the position of theslider and transducer in an off-track direction. Either of the abovemethods of applying the preload force to the slider restricts theoff-track motion of the slider at the suspension load point. When thepreload force is applied to the slider through a dimple, themicroactuator must overcome friction between the dimple and the slidersurface to move the slider in the off-track direction. When the preloadforce is applied to the slider through a gimbal, the microactuator mustovercome the off-track stiffness of the gimbal to move the slider in theoff-track direction.

Improved suspension structures that are adapted for microactuation aredesired.

SUMMARY OF THE INVENTION

The suspension of the present invention includes a longitudinal axis, aproximal mounting section for mounting to a rigid track accessing arm, adistal mounting section for supporting a slider assembly, and first andsecond laterally spaced suspension beams extending from the proximalmounting section to the distal mounting section. The first and secondsuspension beams have inside and outside edges relative to thelongitudinal axis and are flat from the inside edges to the outsideedges. A first preload bend is formed in the first and second suspensionbeams transverse to the longitudinal axis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a disc drive data storage device accordingto one embodiment of the present invention.

FIG. 2A is a top plan view of an actuator assembly of the disc driveshown in FIG. 1.

FIG. 2B is a side plan view of the actuator assembly.

FIG. 2C is a cross-sectional view taken along lines 2C--2C of FIG. 2A.

FIG. 3A is a top plan view of an actuator assembly according to analternative embodiment of the present invention.

FIG. 3B is a side plan view of the actuator assembly shown in FIG. 3A.

FIG. 4 is a top plan view of an actuator assembly having a suspensionattached to a leading end of a slider assembly.

FIGS. 5A and 5B are isometric views of a finite element model of asuspension in the actuator assembly shown in FIG. 3A.

FIG. 6 is a plot of net pitch torsion at an air bearing load pointversus preload bend location.

FIG. 7A is an isometric view of a finite element model of the suspensionin FIG. 3A with a preload bend removed.

FIG. 7B is an "off-track bode plot" of the model shown in FIG. 7A.

FIG. 8A is a side plan view of the model shown in FIG. 5A with a preloadbend positioned at 50 percent of the suspension beam length.

FIG. 8B is an off-track bode plot for the model shown in FIG. 8A.

FIG. 9A is a side plan view of the model shown in FIG. 5A with a preloadbend positioned at 35 percent of the suspension beam length.

FIG. 9B is an off-track bode plot of the model shown in FIG. 9A.

FIG. 10A is a top plan view of an actuator assembly having piezoelectricstrips on suspension preload bends.

FIG. 10B is a side plan view of the actuator assembly shown in FIG. 10A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a plan view of a disc drive 10 according to one embodiment ofthe present invention. Disc drive 10 includes a housing with a base 12and a top cover 14 (sections of top cover 14 are removed for clarity).Disc drive 10 further includes a disc pack 16, which is mounted on aspindle motor (not shown) by a disc clamp 18. Disc pack 16 includes aplurality of individual discs which are mounted for co-rotation about acentral axis. Each disc surface has an associated disc headslider/microactuator assembly 20 which is mounted to disc drive 10 forcommunication with the disc surface. Each slider/microactuator assembly20 is supported by a suspension 22 which, in turn, is supported by arigid track accessing arm 24 of an actuator assembly 26.

The actuator assembly shown in FIG. 1 is of the type known as a rotarymoving coil actuator and includes a voice coil motor (VCM), showngenerally at 28. Voice coil motor 28 rotates actuator assembly 26 withits attached slider/microactuator assemblies 20 about a pivot shaft 30to position slider 20 over a desired data track under the control ofelectronic circuitry 33. Slider/microactuator assembly 20 travels alongan arcuate path 32 between a disc inner diameter (ID) 38 and a discouter diameter (OD) 39.

Suspension 22 is shown in greater detail in FIGS. 2A and 2B. FIG. 2A isa top plan view of the distal end of actuator assembly 26. FIG. 2B is aside plan view of the distal end of actuator assembly 26. Suspension 22has a proximal mounting section 40 (shown in phantom), a distal mountingsection 42, a pair laterally spaced suspension beams 44 and 46 and alongitudinal axis 48. Proximal mounting section 40 is supported by trackaccessing arm 24. A variety of mounting techniques can be used to attachproximal mounting section 40 to track accessing arm 24.

Suspension beams 44 and 46 extend from proximal mounting section 40 todistal mounting section 42 along longitudinal axis 48. Suspension beams44 and 46 terminate at a pair of slider mounting pads 50 and 52,respectively, within distal mounting section 42, for supportingslider/microactuator assembly 20. An optional bridge structure 54extends between slider mounting pads 50 and 52 and includes preformedbends 54A and 54B which raise bridge structure 54 relative to the topsurface of slider/microactuator assembly 20.

The simple block representing slider/microactuator assembly 20 mayinclude a slider body 56 only or slider body 56 in combination with amicroactuator structure 58. In the embodiment shown in FIGS. 2A and 2B,slider mounting pads 50 and 52 are bonded to microactuator structure 58,which suspends slider body 56 beneath bridge structure 54 and free ofphysical contact with bridge structure 56. This allows slider body 56 tomove freely in an off-track direction 59, transverse to longitudinalaxis 48 without frictional or other structural interference fromsuspension 22.

Slider body 56 has a back surface 56a, a bearing surface 56b, a leadingsurface 56c, a trailing surface 56d and side surfaces 56e and 56f. Avariety of microactuators can be used with the present invention, suchas an electromagnetic device on top of slider body 56. Anothermicroactuator device that is well suited for the suspension of thepresent invention is a piezoelectric device deposited on leading surface56a of slider 56. Microactuator structure 48 may alternatively supportslider body 56 along side surfaces 56e and 56f. For example,microactuator structure 58 can suspend slider body 56 between a pair ofbeams 60a and 60b which are attached to a point along side surfaces 56eand 56f. Slider support pads 50 and 52 are bonded to the top surface ofbeams 60a and 60b, respectively. Narrow beam springs located betweenbeam 60a and slider side surface 56e and between beam 60b and sliderside surface 56f support the slider while allowing the slider to movefreely.

Attaching the suspension to the microactuator structure at a pointdistant from the slider body allows the slider body to move freely inthe off-track direction with very little actuation force. FIG. 2C is asectional view taken along lines 2C--2C of FIG. 2A, which shown thespacing between bridge structure 54 and slider body 56 in greaterdetail. In an alternative embodiment, there is no microactuatorstructure, and slider support pads are bonded directly to back surface56a of slider body 56.

In the embodiment shown in FIGS. 2A and 2B, beams 44 and 46 extend alongthe sides of slider/microactuator assembly 20, and the averagelongitudinal location of the beam attachment at slider mounting pads 50and 52 corresponds to an air bearing load point 61 of slider body 56(shown in FIG. 2B).

As the disc rotates beneath air bearing surface 56b, the slider bodypitches and rolls to an equilibrium position wherein a center bearingpressure is defined on the air bearing surface. The desired location ofthe pressure center is defined as the air bearing load point 61.

Slider mounting pads 50 and 52 are attached to microactuator structure58 such that air bearing load point 61 lies substantially directlybetween the suspension beam attachment points. However, this embodimenthas a disadvantage that a number of potential recording tracks cannot beaccessed near the inner diameter of the disc since the suspension beamadjacent the inner diameter must fit between slider/microactuatorassembly 20 and the disc spindle hub. For example if there are 10,000tracks per inch on the disc and suspension beams 44 and 46 extend about0.010 inches from the side of slider/microactuator assembly 20, roughly100 tracks are lost from the inner radius area of the disc.

Suspension 22 has no distinct separation into preload bend, load beamand gimbal areas. Both the preloading and gimbal flexure functions areobtained from suspension beams 44 and 46. Suspension beams 44 and 46 arelonger than typical gimbal struts of the prior art, which results insimilar pitch stiffness. The roll stiffness of suspension beams 44 and46 is higher than typical gimbal struts because the beams are placedfarther apart than typical gimbal struts. The high roll stiffness,however, is compatible with air bearing sliders having a singlerecording head mounted at the center of the trailing surface 56d ofslider body 56. With the recording head mounted at the center oftrailing surface 56d, the flying height of the recording head isrelatively insensitive to roll stiffness.

Suspension 22 is made from a flat stock of stainless steel or similarmaterial which has a thickness from 0.5 to 2.0 mils, for example. Theflat stock of material is lithographically patterned and chemicallyetched to form suspension beams 44 and 46. Suspension 22 has an uppersurface 62 and a lower surface 64, and suspension beams 44 and 46 havean inside edge 66 and an outside edge 68 relative to longitudinal axis48. Suspension 22 has no stiffening webs or flanges along the length ofbeams 44 and 46. Rather, suspension beams 44 and 46 are substantiallyflat from inside edge 66 to outside edge 68.

Suspension beams 44 and 46 have a width W which tapers alonglongitudinal axis 48, with the wide end of the beams being supported bytrack accessing arm 24 and the narrow end of the beams supportingslider/microactuator assembly 20. Width W preferably narrows linearlyfrom a maximum width at track accessing arm 24 to a minimum width atslider assembly 20. In an alternative embodiment, beams 44 and 46 have aconstant width from track accessing arm 24 to slider assembly 20.

A preload bend 80 (shown in FIG. 2B) is formed in suspension beams 44and 46 in a direction transverse to longitudinal axis 48. Preload bend80 becomes elastically deformed (as shown in FIG. 2B) when trackaccessing arm 24, suspension 22 and slider/microactuator assembly 20 areloaded into the disc drive.

Notches 82 and 84 are formed along inside edges 66 of beams 44 and 46for defining a weak point in the beams which aids in consistent locationof preload bend 80 along longitudinal axis 48. Notches 82 and 84 may belocated along inside edges 66 only, outside edges 68 only or along bothinside edges 66 and outside edges 68. Alternatively there may be nonotches used. In the prior art, the preload bend location is typicallyset by the tooling used to form the bend. Variations in tool set-up cancause variations in the preload bend location of about +/-0.06 mm, forexample. Notches 82 and 84 increase the stress level in adjacentmaterial during the preload bend forming process, such that largeplastic deformations occur near the desired bend location. Therefore,the majority of plastic strain defining the preload bend is localized,regardless of variations in tooling. In this manner, the placement ofpreload bend 80 is controlled more accurately than in the prior art.Alternatively, specifications on tool accuracy may be relaxed with asimilar level of bend placement accuracy.

With the tapered suspension beams shown in FIG. 2A, the beams have anearly uniform bending stress level along their length in response toelastic deformation of preload bend 80, except for end effects in thesuspension where the suspension connects to relatively rigid components.In contrast, suspension beams with a constant width have a maximumstress due to the elastic deformation of preload bend 80 at the trackaccessing arm end of the beams, which decreases to a small stress at theslider end of the beams. This maximum stress is determined by the beamwidth which is set by the lithographic masking and chemical etchingprocess. Tapered beams also have less mass for a given maximum bendingstress level and therefore have less tendency to separate from the discsurface under shock loading as compared to constant width beams. If thesuspension beams taper to a point at the air -bearing load point, thebeams will have a minimum mass for a given bending stress level.Substantially all of the suspension material will be at the specifiedbending stress level, so no further mass reductions can be made withoutincreasing the bending stress level above the specified level. Thisresults in the best possible low frequency shock resistance.

Suspension beams 44 and 46 are substantially unconnected to one anotherbetween track accessing arm 24 and slider/microactuator assembly 20.However, suspension 22 may further include minimal tooling features suchas features 72 and 74 (shown in phantom) which extend between thesuspension beams for providing apertures, slots or other features foraiding in the alignment of track accessing arm 24, suspension 22 andslider/microactuator assembly 20 during assembly.

FIGS. 3A and 3B illustrate an actuator assembly 100 in which thesuspension beams are attached to the leading end of slider/microactuatorstructure 20 as opposed to the sides of the assembly, in accordance withan alternative embodiment of the present invention. FIG. 3A is a topplan view of the distal end of actuator assembly 100, and FIG. 3B is aside plan view of actuator assembly 100. The same reference numerals areused for the same or similar elements as were used in FIGS. 1-2.Actuator assembly 100 includes track accessing arm 24,slider/microactuator assembly 20 and suspension 102.

Suspension 102 includes proximal mounting section 106, distal mountingsection 108, laterally spaced suspension beams 110 and 112 andlongitudinal axis 114. Suspension beams 110 and 112 have a preload bend113 formed transverse to longitudinal axis 114. Distal mounting section108 extends over the top surface of slider/microactuator assembly 20 adistance 115 and is bonded to either microactuator structure 58 orslider body 56. In one embodiment, distal mounting section 108 is bondedto the top surface of a main body 58a of microactuator structure 58.Main body 58a has a plurality of electrical terminals 119 (shown inphantom), some of which may be electrically coupled to suspension 102such that suspension 102 acts as a ground plan for the microactuator.The remaining terminals would be coupled to electrical control wires ina known manner. Main body 58a supports slider body 56 through beams 60aand 60b and narrow spring between 60a and 56e and between 60b and 56f.

Suspension beams 110 and 112 have an effective free length L_(F), whichis measured from the distal end of track accessing arm 24 to the leadingend of slider/microactuator assembly 20. Suspension 102 transfers apreload force from the elastically deformed preload bend 113 toslider/microactuator assembly 20 at a suspension load point 116.Suspension load point 116 is defined as the point along longitudinalaxis 114 at which suspension 102 is first connected toslider/microactuator assembly 20 (in this case at the leading end ofassembly 20).

By placing suspension load point 116 forward of the air bearing loadpoint 61, suspension beams 110 and 112 may be placed closer togetherwhich decreases the roll stiffness of suspension 102 and increases thenumber of usable data tracks at the inner radius area of the disc. Thisalso results in a combined preload force and pitch moment being appliedto slider/microactuator assembly 20 at suspension load point 116. Thepitch moment is defined as the preload force times a longitudinaldistance 118 between suspension load point 116 and air bearing loadpoint 61. The correct pitch moment at suspension load point 116 resultsin a desired, substantially zero pitch moment at air bearing load point61.

One method of obtaining the correct pitch moment is to place preloadbend 113 at an appropriate position along the length of suspension beams110 and 112. Notches 122 are formed along inside edges 124 and outsideedges 126 of suspension beams 110 and 112 for accurately defining thelocation of preload bend 113 along length 120. For a set of suspensionbeams having a constant width along length 120, this location was foundto be preferably about 1/3 the distance between track accessing arm 24and suspension load point 116. For a set of tapered suspension beamswith nearly constant bending stress, as described above, this locationwas found to be about 1/2 the distance between track accessing arm 24and suspension load point 116.

FIG. 4 is side plan view of an actuator assembly 140 according toanother alternative embodiment of the present invention. Actuatorassembly 140 includes track accessing arm 24, suspension 142 andslider/microactuator assembly 144. Suspension 142 is bonded to theleading surface of slider/microactuator assembly 144.Slider/microactuator assembly can include a slider body 146 only or,more preferably, can include slider body 146 in combination with amicroactuator structure 148. Microactuator structure 148 is bonded toleading slider surface 150 during head wafer fabrication. Microactuatorstructure 148 is built up by a thick film method and then fired inplace. After dicing the wafer into individual slider bodies, electricalconnections are made to the microactuator electrical terminals.Suspension 142 is then attached to leading surface 152 of microactuatorstructure 148 with the electrical connections interposed betweensuspension 142 and microactuator structure 148 using an insulating epoxyor similar adhesive.

The electrical signals that are applied to the electrical terminalscause microactuator structure 148 to selectively expand and contract therelative distance between suspension 142 and the two ends of leadingslider surface 15C to actuate slider body 144 in an off-track direction.This allows micropositioning of the read or write transducer carried byslider body 144 during read and write operations. Microactuatorstructure 148 may be formed of a piezoelectric material which includes alead zirconate titanate (PZT) material, for example. However, othertypes of microactuators may be used with the present invention, such aselectromagnetic, electrostatic, capacitive, fluidic, and thermalmicroactuators.

As mentioned above, the suspension shown in the previous figures has nostiffened load beam section. Stiffened load beam sections have been usedin suspensions of the prior art to stabilize the dynamic response of theslider/suspension assembly by limiting out-of-plane deflection of thesuspension under preload. The stiffened load beam has served to maintaina substantially planar suspension by limiting the elastic strain of thepreloading to a small length near the track accessing arm. Since thesuspension of the present invention has no stiffened load beam section,the suspension beams have elastic strain due to preloading throughoutthe length the beams, from the track accessing arm to theslider/microactuator assembly. Additional resonance control measures aretherefore desired.

A suspension having tapered beams with vanishing widths at thelongitudinal location of the air bearing load point most closelyapproaches the constant bending stress condition. This ideal can only beapproximated due to bending stress risers at the ends of the suspensionwhere the suspension attaches to relatively rigid components. This alsoprovides a nearly constant curvature along the entire free length of thebeams under elastic loading. If the suspension beams have a preload bendwith a large radius of curvature, the preload bend will reverse underpreloading such that the preloaded suspension will be nearly flat in aplane parallel with the disc. This is the ideal condition for the bestoff-track frequency response of the suspension.

Since it is difficult to form a preload bend such that the entiresuspension beam is uniformly curved, it is more common to have arelatively sharp bend, which forms a "hump" of elastically strainedmaterial under preload as shown in FIGS. 2B, 3B and 4. The position ofthis hump can be varied with the bend forming tool such that the averagedeviation of spring material away from the ideal plane is minimized.

FIGS. 5-9 shown finite element modeling results that were used todetermine a desired preload bend location for a suspension similar tothat shown in FIGS. 3A and 3B. The slider was modeled with a length of56 mils, a width of 42 mils and a mass of 2.0 mg, which is about 35percent of industry standard dimensions. Suspension beams 110 and 112were modeled as if etched from stainless steel flat stock materialhaving a thickness of 1.2 mils. The suspension length from the distalend of the track accessing arm to the air bearing load point was 0.300inches. The distance from the suspension load point 116 at the leadingend of the slider to the air bearing load point 61 at the center ofbearing pressure was 0.033 inches. Suspension beams 110 and 112 weremodeled as tapering to a point having zero width at air bearing loadpoint 61. The mass of the suspension was very small, resulting in a lowfrequency shock acceleration threshold of 651 gravities beforeseparation between the slider and disc occurs. This approached an idealvalue of 1000 gravities for a massless suspension with a 2.0 mg sliderand 2.0 gmf preload. By comparison, a similar assembly using a typicalsuspension of the prior art had a shock acceleration threshold of only340 gravities.

Figure SA is an isometric view of a finite element model of suspension102. Suspension beams 110 and 112 were modeled with the preload bend 113in each beam. Each preload bend 113 had a bend angle 160 of 35.8° and abend radius of curvature of 0.050 inches. Thus, only a portion of thebeam length was formed into a bend. Preload bends 113 were centeredhalfway along the effective free length of the beams, measured from thetrack accessing arm to the leading end of slider/microactuator assembly20. There were no notches used to aid in bend location.

FIG. 5B is an isometric view of the finite element model shown in FIG.5A, after adding an air bearing lifting force 162 applied to the airbearing surface of slider/microactuator assembly 20. The resultingbending stress along suspension beams 110 and 112 was at a uniform levelof 40,000 psi at material locations that were distant from end effects.End clamping at track accessing arm 24 and slider/microactuator assembly20 increased the bending stress at those locations to about 63,000 psi.Since the yield stress of fully hardened stainless steel in this examplewas specified at 180,000 psi, suspension beams 110 and 112 were notoverstressed by preloading.

FIG. 6 is a plot of the net pitch torsion at air bearing load point 61versus the preload bend location along the effective free length ofsuspension beams 110 and 112. As discussed above, it is desirable tohave a nearly zero pitch torsion on the air bearing. Stiffnessvariations in the suspension and the signal wires cause largervariations in a non-zero pitch torsion value than in a zero pitchtorsion value. The plot of FIG. 6 shows that a single preload bend atabout half the effective beam length results in nearly zero pitchtorsion on the air bearing.

FIG. 7A is an isometric view of a finite element model of suspension 102with the preload bend removed. Suspension 102 therefore provides zeropreload force to slider/microactuator assembly 20. With the model shownin FIG. 7A, the suspension material lies in plane parallel with the discsurface when the suspension and slider are loaded into the disc drive.

FIG. 7B is an "off-track bode plot" which illustrates a frequencyresponse amplitude ratio of recording head off-track displacement overthe amount of accessing arm input motion. The suspension modeled in FIG.7A had a single resonant mode of slider yawing at 12.6 KHz. The taperedbeams modeled in FIG. 7A deflect with a constant curvature under a tipload.

Therefore, a preload bend formed with a constant curvature along theentire length of the suspension would deflect to a substantially flatconfiguration as in FIG. 7A when the suspension is loaded into the discdrive. However, such a bend is difficult to obtain in practice, due tospring back effects in the bend forming process.

FIG. 8A is a side plan view of the suspension model shown in FIG. 5A inan unloaded position 164 (shown in phantom) and in a loaded position166, with preload bend 113 positioned at 50 percent of the distancebetween the track accessing arm and the leading end ofslider/microatuator assembly 20. FIG. 8B is a corresponding off-trackbode plot for the suspension model shown in FIGS. 5A-5B. Severaladditional resonant peaks appear due to torsional modes of vibrationwithin the suspension. The lowest frequency of these additional resonantpeaks is 3.0 KHz.

FIG. 9A is a side plan view of the suspension model shown in FIG. 5Awith preload bend 113 positioned at 35 percent of the distance betweenthe track accessing arm and the leading end of slider/microatuatorassembly 20. FIG. 9B is a corresponding off-track bode plot of the modelshown in FIG. 9A. Only two resonant peaks remain, a torsion moderesonant peak at 4.0 KHz and a slider yaw mode resonant peak at 14.5KHz.

Thus, the result shown in FIG. 9B suggest that the preload bend 113 bepositioned at 35 percent of the suspension beam length to obtain anoff-track bode plot with minimal resonant peaks, while the results shownin FIG. 6 suggests that the preload bend 113 be positioned at so percentof the suspension beam length to obtain zero pitch torsion at the airbearing load point. A suspension having a minimal mass and a singlepreload bend of a small radius of curvature therefore cannot give thedesired combination of zero pitch torsion at the air bearing load pointand an off-track bode plot with minimal resonant peaks.

Several solutions to this dilemma are possible in accordance with thesuspension of present invention. First, the suspension can have a planform other than the minimal mass configuration (which is shown in FIG.3A). This solution would tend to undesireably reduce the shock thresholdat which slider-disc separation occurs. Second, an additional bend canbe formed in suspension beams 110 and 112 near suspension load point114. The additional bend would be formed such that there issubstantially zero pitch torsion at the air bearing load point 61. Thissolution would tend to increase the manufacturing cost due to theadditional bend. Third, the stacking height at the track accessing armcan be increased. The stacking height is equal to the distance from thesurface of the disc to the lower surface of the track accessing arm.Increasing the stacking height tends to reduce nose-down pitch torsionon slider assembly 20.

FIG. 10A is a top plan view of an actuator assembly 190 according toanother alternative embodiment of the present invention. Actuatorassembly 190 includes suspension 200, track accessing arm 202 and slider204. As in the previous embodiments, suspension 200 includes laterallyspaced suspension beams 206 and 208 which extend along longitudinal axis210, between track accessing arm 202 and slider 204. However, in thisembodiment, suspension beams 206 and 208 are attached directly to theback surface of slider 204.

FIG. 10B is a side plan view of actuator assembly 190. An elasticallydeformed preload bend 214 is formed in suspension beams 206 and 208 in adirection transverse to longitudinal axis 210. Piezoelectric strips 216and 218 are attached to suspension 200 along the length of suspensionbeams 206 and 208, respectively. Piezoelectric strips 216 and 218 arepositioned over the "humps" in suspension beams 206 and 208 which arethe resultant shape of the elastically deformed preload bends 214.Piezoelectric strips 216 and 218 can be formed of a polymer such aspolyvinylidene fluoride (PVDF) CH₂ -CF₂.

Piezoelectric strips 216 and 218 are attached to suspension beams 206and 208 with a conductive adhesive such that suspension 200 acts as aground plane for each strip. Each strip has a thin electrode layerdeposited on its top surface, to which control wires or flex circuittraces (not shown) can be bonded. Piezoelectric strips 216 and 218 havepoles that are orientated such that the length of strips 216 and 218along longitudinal axis 212 will expand when a positive voltagepotential is applied between the top electrode and the ground plane andwill contract when a negative voltage potential is applied between thetop electrode and the ground plane.

Strips 216 and 218 act as a self-contained track-seeking microactuatorand preload control device. Since strips 216 and 218 are bonded to thehumps on suspension beams 206 and 208, the hump on a first beam may beflattened by contracting its strip while the hump on the second beam maybe exaggerated by expanding its strip. This action extends the length ofthe first-beam while shortening the length of the second beam, causingslider 204 to shift its track registration in an off-track direction220. The combination of contraction on one suspension beam and expansionon the other suspension beam also changes the preload applied by eachsuspension beam. The following table shows four general modes ofmicroactuation for track seeking and preload control:

    ______________________________________                                        BEAM 206  BEAM 208    PRELOAD    TRACKING                                     VOLTAGE   VOLTAGE     CHANGE     CHANGE                                       ______________________________________                                        -         -           Reduced    None                                         +         -           None       Seek to Beam                                                                  208 Side                                     -         +           None       Seek to Beam                                                                  206 Side                                     +         +           Increased  None                                         ______________________________________                                    

These modes of microactuation may be used in combination to maintain adesired flying stability during track seeking. The preload control modesmay be used alone to allow a relatively high flying height with a lowpreload force when the disc drive is idle, or to allow a low flyingheight with a high preload force when the disc drive is accessing data.The track seeking microactuation mode may be used in a traditionalmanner for centering the recording head on a desired data track or forgenerating a slider/disc stiction release jogging motion during slidertake-off from the disc surface. The preload control modes may be used toload and unload slider 204 from the disc during start up and shut down,as well as to control flying height.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A suspension for supporting a slider in a discdrive, the suspension comprising:a longitudinal axis; a proximalmounting section for mounting to a rigid track accessing arm; a distalmounting section for supporting a slider assembly; first and secondlaterally spaced suspension beams extending from the proximal mountingsection to the distal mounting section, wherein the first and secondsuspension beams have inside and outside edges relative to thelongitudinal axis and are flat from the inside edges to the outsideedges as the beams extend from the proximal mounting section to thedistal mounting section; and a first preload bend formed in the firstand second suspension beams transverse to the longitudinal axis.
 2. Thesuspension of claim 1 wherein the suspension is formed of a single,unitary piece of material.
 3. The suspension of claim 1 wherein:thefirst and second suspension beams have an effective free length which ismeasured from the proximal mounting section to the distal mountingsection; and the first preload bend is positioned between 30 percent and50 percent of the effective free length.
 4. The suspension of claim 3wherein the first and second suspension beams have a substantiallyconstant width from the proximal mounting section to the distal mountingsection.
 5. The suspension of claim 4 wherein the first preload bend ispositioned at about 50 percent of the effective free length.
 6. Thesuspension of claim 3 wherein the first and second suspension beams eachhave a width which decreases linearly between the proximal mountingsection and the distal mounting section.
 7. The suspension of claim 6wherein the first preload bend is positioned at about 35 percent of theeffective free length.
 8. The suspension of claim 7 and furthercomprising:a second preload bend formed in the first and secondsuspension beams, between the first preload bend and the distal mountingsection.
 9. The suspension of claim 1 wherein the first and second beamshave a geometry selected such that a specified bending force applied tothe first and second suspension beams results in a specified bendingstress level in the first and second suspension beams which issubstantially uniform along the first and second suspension beams. 10.The suspension of claim 9 wherein the first and second suspension beamshave a minimum mass such that substantially no material may be removedfrom the first and second suspension beams without increasing bendingstress in the first and second beams beyond the specified bending stresslevel.
 11. The suspension of claim 1 wherein the distal mounting sectioncomprises a first mounting pad formed at a distal end of the firstsuspension beam, a second mounting pad formed at a distal end of thesecond suspension beam and a bridge extending between the first andsecond mounting pads.
 12. The suspension of claim 1 and furthercomprising:a first notch positioned along one of the inside and outsideedges of the first suspension beam and defining a position of the firstpreload bend in the first suspension beam along the longitudinal axis;and a second notch positioned along one of the inside and outside edgesof the second suspension beam and defining a position of the firstpreload bend in the second suspension beam along the longitudinal axis.13. The suspension of claim 1 and further comprising:a firstpiezoelectric microactuator strip applied to the first suspension beamalong the first preload bend; a second piezoelectric microactuator stripapplied to the second suspension beam along the first preload bend; andwherein the first and second piezoelectric strips each have a lengthalong the longitudinal axis which is a function of a voltage applied tothat piezoelectric strip.
 14. An actuator assembly comprising:a rigidtrack accessing arm; a slider assembly; and a suspension comprising:alongitudinal axis; a proximal mounting section supported by the rigidtrack accessing arm; a distal mounting section supporting the sliderassembly; first and second laterally spaced suspension beams extendingfrom the proximal mounting section to the distal mounting sectionthrough substantially an entire distance between the rigid trackaccessing arm and the slider assembly, wherein the first and secondsuspension beams have inside and outside edges relative to thelongitudinal axis and are flat from the inside edges to the outsideedges; and a first preload bend formed in the first and secondsuspension beams transverse to the longitudinal axis.
 15. The actuatorassembly of claim 14 wherein the first and second beams aresubstantially unconnected to one another between the track accessing armand the slider assembly.
 16. The actuator assembly of claim 15 whereinthe suspension further comprises a fixture alignment feature extendingbetween the first and second suspension beams at a location between thetrack accessing arm and the slider assembly.
 17. The actuator assemblyof claim 14 wherein the distal mounting section comprises a firstmounting pad formed at a distal end of the first suspension beam andbonded to the slider assembly, a second mounting pad formed at a distalend of the second suspension beam and bonded to the slider assembly, anda bridge extending between the first and second mounting pads.
 18. Theactuator assembly of claim 17 wherein the slider assembly comprises aslider body with a bearing surface and a back surface and wherein thefirst and second mounting pads are bonded to the back surface of theslider body.
 19. The actuator assembly of claim 17 wherein the sliderassembly comprises a slider body and a microactuator structure andwherein the first and second mounting pads are bonded to themicroactuator structure, which is bonded to the slider body, so as toform a preload force transmission path from the suspension to themicroactuator structure and from the microactuator structure to theslider body.
 20. The actuator assembly of claim 19 wherein:the sliderbody has first and second side surfaces and a back surface; themicroactuator structure is bonded to the slider body at the first andsecond side surfaces; the first and second mounting pads are attached tothe microactuator structure adjacent the first and second side surfaces,respectively; and the bridge extends over the back surface of the sliderbody and is formed out-of-plane with the first and second mounting padssuch that the bridge is separated from the back surface.
 21. Theactuator assembly of claim 20 wherein:the slider body further has alength along the longitudinal axis and a bearing surface, wherein thebearing surface defines a bearing load point along the length; and thefirst and second mounting pads each have an average longitudinal bondlocation along the length which corresponds to the bearing load point.22. The actuator assembly of claim 19 wherein:the slider body has aleading end and a trailing end is parallel with the longitudinal axis ofthe suspension; the microactuator structure comprises a main body with asuspension mounting surface which is positioned forward of the leadingend of the slider body, along the longitudinal axis, and comprises atleast one beam spring extending from the main body and attached to theslider body; and the first and second mounting pads are attached to thesuspension mounting surface.